Our general aim is to obtain an understanding of the cellular basis for abdominal positioning behavior using the crustacean model system. Our working hypothesis is that command neurons play a central role in this behavior, that they operate in synaptically interactive groups and that they themselves serve to distribute the necessary excitation aims are: 1) To continue to investigate with dye-filled microelectrodes the organization of abdominal positioning interneurons. The result should help explain how organization, which is important in all nervous systems, contributes to behavior. The accompanying morphological data will add to our current understanding of commands as identified cells and serial homologues. 2) We wish to continue to map the receptive fields and modalities of the inputs to these interneurons. These data will help explain how reflexive positioning might be brought about. 3) We will examine further the nature of synaptic interactions among functionally similar as well as dissimilar pairs and mechanisms of exclusion of simultaneous but incompatible behaviors. We will also look further into the synaptic interactions that occur between command cells and motoneurons. 4) We wish to continue to study of command neuron activity during voluntary behavior. This study will tell us whether some or all of the flexion commands fire during voluntary flexion, whether any one is sufficient or necessary, but most important, it will reveal information on those that initiate abdominal positioning behavior.